The present invention relates to an integral process that uses a minimum number of process steps for producing chemical and high purity grades of lithium carbonate and lithium chloride directly from the same natural brine source.
It is desirable, from a commercial standpoint, to provide a source of lithium low in sodium content because sodium becomes reactive and potentially explosive in certain chemical processes, particularly those in production of lithium metal from lithium salts. A substantial portion of presently available lithium is recovered from brines, which also contain high levels of sodium, making the production of low sodium lithium salts difficult and expensive. At the present time, there does not exist a viable low cost integral processes for producing low sodium lithium carbonate and chemical and high purity grades of lithium chloride directly from natural brines containing lithium.
Natural brines that contain lithium also contain many constituents as illustrated in the following Table:
Production of lithium carbonate and lithium chloride with acceptable qualities from such brines requires employing techniques to remove specific cations and anions that accompany the lithium in solution, and then concentrating the lithium for extraction.
Individual applications require that these ion impurities be reduced to specific maximum levels and a number of processes have been described for removing these impurities. For example, U.S. Pat. No. 5,219,550 to Brown and Boryta describes a method for producing chemical grade lithium carbonate from natural lithium containing brine by first removing most of the components from the brine by concentrating utilizing solar evaporation techniques. Concentrating the brine with respect to lithium by solar evaporation causes most of the unwanted components to precipitate from the brine, i.e., salt out. Boron, which concentrates with the lithium, is subsequently removed using an extraction process. The remaining magnesium is removed by adding a base to precipitate magnesium carbonate and/or magnesium hydroxide, and the lithium is finally precipitated from the purified brine as lithium carbonate by the addition of soda ash. Other processes related to the above process are disclosed in U.S. Pat. Nos. 4,036,718; 4,243,392; and 4,261,960.
Other techniques for producing purified lithium salts are known. For example, German Patent DE 19,541,558 to Wusson et al describes a process to reduce sodium from lithium chloride solutions by cooling. U.S. Pat. No. 4,859,343 to Kullberg et al describes an ion exchange method for removing sodium from brines. U.S. Pat. No. 5,599,516 and Russian Patent No. 9,419,280 describe absorption/ion exchange processes for recovering lithium from brine.
U.S. Pat. No. 4,980,136 discloses a procedure for preparing chemical grade and low sodium lithium chloride (battery grade, less than 20 ppm sodium and less than 5 ppm magnesium) from concentrated natural brine by crystallizing lithium chloride from a magnesium/lithium chloride brine to produce a chemical grade of lithium chloride crystal. This is followed by alcoholic extraction of the soluble lithium chloride from the crystal leaving sodium chloride as the insoluble phase. The alcohol solution containing the lithium chloride is then filtered and evaporated to form a high purity grade of lithium chloride crystal.
East German Patent DD 257,245 describes a method for recovering lithium chloride from concentrated brine containing both calcium chloride and magnesium chloride and selectively extracting lithium chloride with alcohol. Other patents related to such processes include U.S. Pat. Nos. 4,271,131 and 4,274,834.
U.S. Pat. No. 4,207,297 describes production of a low sodium lithium carbonate (sodium less than 10 ppm in lithium carbonate) from technical lithium carbonate. This is accomplished by reacting lithium carbonate with lime followed by filtration to produce a lithium hydroxide solution. The solution is subsequently purified with just enough carbon dioxide to remove the residual calcium and filtered. More carbon dioxide gas is added to the purified lithium hydroxide solution to re-precipitate lithium carbonate crystal as a high purity product.
Except for the methods described in DE 19,541,558, U.S. Pat. No. 4,243,392 and 5,219,550, the methods of the prior art are not practiced today because they are either technically or economically not viable.
Another process for producing lithium chloride is set forth in Chilean Patent Application No. 550-95, which describes a procedure whereby a purified brine containing essentially lithium chloride is directly produced from natural brines that have been concentrated by solar evaporation and treated by an extraction process to remove boron. However, the sodium, calcium, and sulfate levels in the resultant brine are too high to be an acceptable brine source of lithium chloride for producing a technical grade lithium metal, primarily because the two major remaining impurities, sodium and magnesium, have to be further reduced to acceptable levels to produce chemical grade lithium chloride crystal. Specifically, magnesium must be reduced to less than 0.005 wt % Mg, and sodium to less than 0.16 wt % Na in the anhydrous lithium chloride salt. Salting out anhydrous lithium chloride directly from brine above 110xc2x0 C. in a vacuum crystallizer as described in U.S. Pat. No. 4,980,136 yields a lithium chloride containing at best 0.07 wt % Mg and 0.17 wt % Na.
It is accepted, although not proven, that lithium chloride crystal containing 0.07 wt % Mg may be too high in magnesium to be used for producing lithium metal and for subsequent use in the production of lithium organometallic compounds. Thus, the industry demands that organolithium catalysts in polymerization reactions be low in magnesium. Lithium chloride high in magnesium can also adversely affect the operation of the lithium electrolysis cell when producing the lithium metal.
As noted above, the sodium impurity in the lithium chloride crystal reports directly to the metal when producing lithium metal. Thus, low sodium lithium salts are desirable. Sodium in lithium chloride crystal above 0.6 wt % produces metal containing 1 wt % sodium or higher. Sodium concentrations of about 1 wt % in lithium metal or above renders the lithium metal more reactive to natural components of air. This makes the metal more difficult and more dangerous to handle. Table 2 sets forth data concerning sodium limits and tolerances in different lithium sources:
Commercial methods employed to produce low sodium lithium carbonate and lithium chloride on a commercial scale include extraction of lithium compounds from mineral deposits such as spodumene bearing ore and natural brines. A number of processes have been described and some have been commercialized for producing lithium carbonate from these sources.
One such commercial method involves extraction of lithium from a lithium containing ore or brine to make a pure lithium sulfate solution such as described in U.S. Pat. No. 2,516,109, or a lithium chloride solution such as described in U.S. Pat. No. 5,219,550. After purifying the solutions, sodium carbonate is added as either a solid or a solution to precipitate lithium carbonate crystals. The lithium carbonate is subsequently filtered from the spent liquor (mother liquor), and the lithium carbonate is washed, dried, and packaged.
Lithium carbonate is often used as a feed material for producing other lithium compounds such as lithium chloride, lithium hydroxide monohydrate, lithium bromide, lithium nitrate, lithium sulfate, lithium niobate, etc. Lithium carbonate itself is used as an additive in the electrolytic production of aluminum to improve cell efficiency and as a source of lithium oxide in the making of glass, enamels, and ceramics. High purity lithium carbonate is used in medical applications.
For example, a presently used commercial procedure for producing chemical grade lithium chloride is to react a lithium base such as lithium carbonate or lithium hydroxide monohydrate with concentrated hydrochloric acid to produce a pure lithium chloride brine. The resultant lithium chloride brine is evaporated in a vacuum crystallizer at or above 100xc2x0 C. to produce an anhydrous lithium chloride crystal product. This procedure yields a product that meets most commercial specifications for chemical grade lithium chloride, but not low sodium grades of lithium chloride. Chemical grade lithium chloride is suitable for air drying applications, fluxes, an intermediate in manufacture of mixed ion-exchange zeolites, and as a feed to an electrolysis cell for producing chemical grade lithium metal. Chemical grade lithium metal is used, inter alia, to produce lithium organometallic compounds. These compounds are used as a catalyst in the polymerization and pharmaceutical industry.
Chemical grade anhydrous lithium chloride should contain less than 0. 16% sodium in order to produce metal containing less than 1% sodium. The importance of minimizing the sodium content in the metal and the costs associated therewith are the principle reasons for using lithium hydroxide monohydrate or lithium carbonate as the raw material for producing lithium chloride and, subsequently, lithium metal. In consideration, low sodium lithium chloride, typically contains less than 0.0008 wt % sodium, and is commercially produced to manufacture low sodium lithium metal suitable for battery applications and for producing alloys.
Commercially, low sodium lithium chloride is produced indirectly from chemical grade lithium carbonate. Chemical grade lithium carbonate is produced from Silver Peak Nevada brine, Salar de Atacama brines in Chile, Hombre Muerto brines in Argentina, and from spodumene ore (mined in North Carolina). The lithium carbonate is converted to lithium hydroxide monohydrate by reaction with slaked lime. The resultant slurry contains precipitated calcium carbonate and a 2-4 wt % lithium hydroxide solution, which are separated by filtration.
The lithium hydroxide solution is concentrated in a vacuum evaporation crystallizer in which the lithium hydroxide monohydrate is crystallized, leaving the soluble sodium in the mother liquor solution. The crystal lithium hydroxide monohydrate is separated from the mother liquor and dried. This salt normally contains between 0.02 and 0.04% sodium. To further reduce the sodium levels, the lithium hydroxide monohydrate must be dissolved in pure water and recrystallized, and subsequently reacted with pure hydrochloric acid to form a concentrated lithium chloride brine containing less than 10 ppm sodium. The resultant lithium chloride solution is then evaporated to dryness to yield anhydrous lithium chloride suitable for producing battery grade lithium metal containing less than 100 ppm sodium. The above process requires seven major processing steps described as follows:
1) Extraction and purification of a low boron aqueous solution containing 0.66 to 6 wt % Li from lithium containing ore or natural brine;
2) Purification of the brine with respect to magnesium and calcium and filtered;
3) Precipitation of lithium carbonate from the purified brine by addition of Na2CO3, and filtering and drying the lithium carbonate;
4) Reacting slaked lime and lithium carbonate to produce a LiOH solution and filtering;
5) Crystallizing LiOH.H2O in a vacuum crystallizer;
6) Dissolving the LiOH.H2O crystals and re-crystallizing LiOH.H2O from solution; and
7) Reacting high purity HCl with re-crystallized LiOH.H2O to produce a high purity lithium chloride brine from which low sodium lithium chloride is crystallized and drying the lithium chloride.
Low sodium lithium carbonate can be prepared from re-crystallized LiOH.H2O using the first part of the process described above. The recrystallized LiOH.H2O is then mixed with water and reacted with CO2 to precipitate the lithium carbonate. The processing steps are set forth below:
1) Extraction and purification of a low boron aqueous solution containing 0.66 to 6 wt % Li from lithium containing ore or natural brine;
2) Purifying the brine is then purified with respect to magnesium and calcium and filtered.
3) Precipitate Li2CO3 from the purified brine with the addition of Na2CO3, filtered and dried.
4) React slaked lime and Li2CO3 to produce a LiOH solution and filter.
5) LiOH.H2O is crystallized in a vacuum crystallizer.
6) Dissolve again and re-crystallize LiOH.H2O from solution.
7) React CO2 gas with a slurry containing re-crystallized LiOH.H2O to Crystallize low sodium high purity Lithium carbonate crystal, filter and dry.
Production of lithium chloride direct from concentrated brine has also been described in U.S. Pat. No. 4,274,834.
The present invention provides an integral and novel process which reduces the number of major processing steps for producing chemical (technical) grade and low sodium lithium carbonate and lithium chloride directly from natural lithium containing brines concentrated to about 6.0 wt % Li without the lithium hydroxide monohydrate single and double recrystallization steps present in the processes of the prior art.
The present invention also relates to a method for preparing chemical grade lithium chloride direct from the same concentrated starting brine as that used to prepare the lithium carbonate.
The present invention incorporates the process described in U.S. Pat. No. 5,219,550 to produce a chemical grade lithium carbonate to specifically utilize the mother liquor by-product stream from that process to recover lithium from the magnesium containing purification muds that are formed when producing lithium chloride directly from brine, eliminating the steps of first precipitating lithium carbonate or lithium hydroxide and then transforming these salts to lithium chloride. Additionally, the process of the invention yields a high purity lithium carbonate having less than about 0.002 wt % sodium using a carbon dioxide/bicarbonate cycle, and a process of preparing a high purity lithium chloride by reacting the high purity lithium carbonate with a high purity hydrochloric acid.
All patents cited herein are incorporated by reference in their entireties.